This invention relates to a concrete column forming tube and method of forming a poured concrete column which is characterized by and incorporates an improved device for aiding in removing the forming tube from the concrete column produced therein.
For many years, concrete column forming tubes have been utilized and have been constructed of spirally-wound plies of paper adhered together and defining an inside wall surface of predetermined diameter which is coated with plastic material for concrete release properties. This plastic coating was usually provided by coating one side of the paper plies prior to spiral winding of the tube. These forming tubes received poured concrete therein which dried and set-up to produce a concrete column. The forming tube was then striped away from the concrete column and this operation was aided by the release properties of the plastic coating on the inside of the tube to leave a finished concrete column. These types of prior art tubes are disclosed in U.S. Pat. Nos. 2,677,165 and 2,914,833, for example, which are assigned to the assignee of the present invention.
Due to the spirally-wound construction of these forming tubes, spiral seam lines and other undesirable surface characteristics were usually present on the inside wall surface of the forming tube which resulted in spiral seam lines and other irregularities being molded on the outside surface of the produced concrete column. From an aesthetic standpoint, these spiral seam lines and other irregularities were usually undesirable on the produced concrete column and sandblasting or other finishing techniques were necessary to produce a smooth outside surface on the concrete columns.
In an effort to overcome these problems, concrete column forming tubes with separately-formed flexible cylindrical liners have been proposed by U.S. Pat. No. 4,595,168 and Assignee""s U.S. Pat. No. 4,957,270. These separate liners were inserted into the concrete column forming tube after manufacture of the tube and often at the concrete column forming site. While these separate liners improved the surface quality of the resulting concrete column, they did often produce one vertical seam line running the length of the formed column, were expensive to manufacture, difficult to maintain and install, and presented other problems in the manufacture and use thereof.
More recently, these problems have been overcome by a concrete column forming tube construction as set forth in Assignee""s U.S. Pat. No. 5,874,016 wherein a centrifugally-cast epoxy resin coating is sprayed onto the inside wall surface of a spirally-wound paper tube while the tube is rotating. This coating has a sufficiently low viscosity to produce an inside coated surface on the forming tube which extends continuously across the spiral seam lines and has a thickness and smoothness sufficient to eliminate spiral seam lines and other undesirable characteristics on the inside surface of the tube and on an outside surface of the formed concrete column. While this concrete column forming tube construction overcame these problems of spiral seam lines and other irregularities on the produced concrete column, it has been determined that these concrete column forming tubes are difficult to remove from the formed concrete column.
The problem of removal of concrete column forming tubes from the formed concrete column has been considered in the above-mentioned, Assignee""s U.S. Pat. No. 2,677,165 wherein two diametrically opposed cutting wires are arranged on the inside surface of the concrete column forming tube. These cutting wires extend over the entire length of the concrete column forming tube and are used to tear open the tubular mold and to divide it into sections when it is desired to remove the concrete column forming tube from the formed concrete column. However, these cutting wires form longitudinally extending lines on the outside surface of the poured or formed concrete column and, thus, produce disadvantages in addition to those discussed above with respect to the undesirable spiral seam lines and other irregularities.
This latter problem of removal of the concrete column forming tube from the formed concrete column has also been addressed in German Utility Model Patent G 89 05 989.1, published Aug. 17, 1989, wherein a thread like or band-shaped ripping element was provided along the inside wall of the concrete column forming tube for ripping open the concrete column forming tube after the concrete column has been poured or formed. In the concrete column forming tube of this German Utility Model Patent, spiral seam lines and an image of the ripping element will be produced on the outside surface of the finished concrete column.
Accordingly, it is the object of this invention to provide a concrete column forming tube for receiving poured concrete therein to produce a concrete column and which overcomes all of the problems set forth above by eliminating spiral seam lines and other undesired characteristics on an outside surface of the formed concrete column and by providing a construction which may be more easily removed from the formed concrete column.
By this invention, it has been found that the above object may be accomplished by providing a concrete column forming tube which is constructed of spirally-wound plies of paper adhered together and defining an inside wall surface having spiral seam lines thereon, and a centrifugally-cast plastic coating sprayed on the inside surface of the spirally-wound paper tube while the tube is rotating for producing an inside coated surface on the forming tube which eliminates spiral seam lines and other undesirable characteristics. A tear strip is positioned between the inside surface of the cylindrical paper tube and the plastic coating (prior to centrifugal-casting thereof) so as not to interfere with the smoothness of the inside coated surface of the forming tube. The tear strip extends longitudinally of the column forming tube over the entire length of the column forming tube. The tear strip has a predetermined width and is readily detachable from the plastic coating. In a preferred embodiment, a dent is pressed into the inside surface of the spirally-wound paper tube for receipt of the tear strip, so that the thickness of the plastic coating needed to produce a smooth inside surface in the forming tube can be reduced.
When it is desired to remove the forming tube from the concrete column produced, the tear strip is pulled from one end of the forming tube to the other end to tear open and remove a section of the cylindrical paper tube to produce a longitudinally-extending gap therein of a width generally equal to the predetermined width of the tear strip to receive or accommodate therein a device for cutting through the remaining plastic coating. Preferably, the tear strip is rolled-up on a longitudinally-extending instrument along with the section of paper tube being removed during opening of the forming tube. This device for cutting through the plastic coating may comprise a heat-omitting device or the blunt edge of a cutting instrument, etc.
Preferably, the tear strip is a reinforced plastic material and, more preferably, a glass fiber reinforced plastic tape. Preferably, the centrifugally-cast plastic coating on the inside surface of the spirally-wound paper tube is a thermoplastic material, and more preferably, a polyurethane. A continuous wire may be positioned in each longitudinal edge of the tear strip. The tear strip is preferably at least 10 mm in width and, more preferably, between 10 and 50 mm in width. The concrete column forming tube may include two tear strips positioned at 180xc2x0 of each other to facilitate removal of the forming tube from the concrete column.